The present invention relates to a method and apparatus for locating and evaluating geothermal sources of energy and more particularly to such a method and apparatus which are operable at a small fraction of the expense of conventional methods and apparatus in locating geothermal sources of commercial potential with the capability of evaluating vast territories rapidly, efficiently, and with a precision not heretofore achievable at a commercially acceptable expense.
The few prior art patents, such as the Blau U.S. Pat. No. 2,403,704 and Birman U.S. Pat. No. 3,217,550, relate primarily to methods and/or apparatus requiring the drilling of exploratory boreholes to permit the recording of subsurface temperatures. Such prior art practices are subject to deficiencies which the method and apparatus of the present invention have overcome.
As pointed out in joint applicant Sayer's copending patent application, Ser. No. 325,657, filed Jan. 22, 1973, geothermal anomalies, that is subterranean sources of heat energy, have long been recognized as a potentially almost unlimited source of energy. Geothermal anomalies are often manifest in the form of subterranean bodies of naturally super heated water or steam. Whether or not ambient fluid is present at the source is not of primary importance, however, since it is known to pump surface water to such sources for heating to permit the subsequent extraction of energy from the water. Thus, it is the location of the geothermal source itself which is of paramount importance.
The approximate location of such sources is sometimes apparent in the presence on the surface of the earth of such phenomena as geysers and fumaroles. However, it is extremely difficult to locate the sources of such surface features because they are frequently connected to the surface through intricate underground passages or vents leading from the surface to the source at great depth and sometimes laterally disposed with respect to the surface phenomena. Furthermore, it has been discovered that abundant geothermal sources lie at depths in the earth in areas where there is an absence of surface features which would make their presence readily apparent.
Conventional practice requires the performance of laborious and extremely expensive surveys in order adequately to evaulate even quite limited areas. Such surveys commonly require the drilling of a plethora of trial boreholes and the recording of temperatures at the bottoms of such boreholes. This is normally inordinately expensive and frequently proves to be fruitless. Thus, the harnessing of geothermal energy has been of only limited success due to the difficulty in accurately and efficiently locating the sources of such energy at a commercially acceptable cost rather than in bringing such sources into production once located.
Therefore, it has long been recognized that it would be desirable to have a method and apparatus capable of accurately, inexpensively and dependably locating sources of geothermal energy of commercial significance.